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use basecase division for short power series divisions

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Fredrik Johansson 2016-03-12 03:12:38 +01:00
parent d1ac8dc4b9
commit e8b9100478
2 changed files with 60 additions and 0 deletions
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30
acb_poly/div_series.c
View file

@ -54,6 +54,36 @@ _acb_poly_div_series(acb_ptr Q, acb_srcptr A, slong Alen,
acb_div(Q + 1, Q + 1, B, prec);
}
}
else if (Blen == 2 || n <= 10)
{
/* The basecase algorithm is faster for much larger Blen and n than
this, but unfortunately has worse numerical stability. */
slong i, j;
acb_t q;
acb_init(q);
acb_inv(q, B, prec);
acb_div(Q, A, B, prec);
for (i = 1; i < n; i++)
{
acb_mul(Q + i, B + 1, Q + i - 1, prec);
for (j = 2; j < FLINT_MIN(i + 1, Blen); j++)
acb_addmul(Q + i, B + j, Q + i - j, prec);
if (i < Alen)
acb_sub(Q + i, A + i, Q + i, prec);
else
acb_neg(Q + i, Q + i);
if (!acb_is_one(q))
acb_mul(Q + i, Q + i, q, prec);
}
acb_clear(q);
}
else
{
acb_ptr Binv;

30
arb_poly/div_series.c
View file

@ -54,6 +54,36 @@ _arb_poly_div_series(arb_ptr Q, arb_srcptr A, slong Alen,
arb_div(Q + 1, Q + 1, B, prec);
}
}
else if (Blen == 2 || n <= 10)
{
/* The basecase algorithm is faster for much larger Blen and n than
this, but unfortunately has worse numerical stability. */
slong i, j;
arb_t q;
arb_init(q);
arb_inv(q, B, prec);
arb_div(Q, A, B, prec);
for (i = 1; i < n; i++)
{
arb_mul(Q + i, B + 1, Q + i - 1, prec);
for (j = 2; j < FLINT_MIN(i + 1, Blen); j++)
arb_addmul(Q + i, B + j, Q + i - j, prec);
if (i < Alen)
arb_sub(Q + i, A + i, Q + i, prec);
else
arb_neg(Q + i, Q + i);
if (!arb_is_one(q))
arb_mul(Q + i, Q + i, q, prec);
}
arb_clear(q);
}
else
{
arb_ptr Binv;